Title

Potentiometric Titrations of Proteins and Polypeptides in Concentrated Salt Solutions

Publication Year

1969

Keywords

proteins, enzymes, potentiometric titrations, biophysical chemistry, chemistry, polypeptide behavior

Disciplines

Biochemistry, Biophysics, and Structural Biology | Chemistry | Physical Sciences and Mathematics

Abstract

The potentiometric titration curves have been obtained for Poly-L-Arginine, Poly-L-Aspartic Acid, Poly-L-Glumatic Acid, Poly-L-Histidine, Poly-L- Lysine, Poly-L-Ornithine, and Poly-L-Tyrosine. These homopolymers were studied in CsCl with the exception of Poly-L-Aspartic which was studied in Cs2SO4. The apparent dissociation constants increased as the salt concentration increased. Densities of the titrated solution ranged from mean = 1.00 g/ml to mean = 1.85 g/ml. The alpha helix to random transition was found to depend upon the pH and the salt concentration.

The continuous titration curves of four copolymers were obtained. L-Glutamic:L-Tyrosine, L-Lysine:L-Tyrosine, L-Alanine:L-Tyrosine, and L-Glutamic Acid:L-Lysine were studied. The apparent pK's were found to depend on amino acid composition, hydrogen bonding, salt bridges, and ionic strength.

The potentiometric results were correlated with the buoyant density titrations that were available.

The intrinsic dissociation constants of the carboxyl residues of Bovine Serum Albumin, BSA, have been obtained at low salt concentrations. The hydrogen ion dissociation curves have been determined up to 2.60 M KCl in both the acidic and basic regions. The carboxyl intrinsic dissociation constants were found to increase with increasing ionic strengths. The hydrogen ion dissociation curves in the acidic region shifted to higher pH's with increased salt concentrations. Separate and continuous titration methods were applied to BSA. Calculations were done by an IBM 1130 Digital computer.

Department 1 Awarding Honors Status

Chemistry

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